Project Summary/Abstract It has long been known that diabetes mellitus causes damage to the retina and lens. Recent evidence suggests that diabetes also affects tear film and causes dry eye. The long-term goal of the project is to understand how diabetes mellitus causes dry eye disease with the intention to identify mechanism-based therapeutic approaches for its treatment or prevention. A normal tear film has lipid, aqueous and mucous layer contributed by meibomian glands, lacrimal gland and ocular surface cells, respectively. Diabetes-mediated abnormality in any of the three layers individually or collectively can cause dry eye. The specific goal of the current application is to determine how diabetes mellitus alters mucous layer of the tear film to cause dry eye disease. Mouse models of type I and type II diabetes will be utilized in this proposal to quantify the time course changes in tear secretion, tear osmolarity and ocular surface glycocalyx integrity. Apoptosis of corneal and conjunctival epithelial cells and a decrease in goblet cell density due to diabetes mellitus will also be measured in the tissues obtained from these mice. Mucins will be quantified by ELISA in the tears obtained from these mice. Mucins gene expression will be quantified by real time PCR using the cDNA obtained from the cultured human corneal and conjunctival epithelial cells exposed to high glucose. Finally, mice will be given insulin to maintain normal blood glucose levels right at the onset of diabetes or at 4 weeks after diabetes. The outcome of these experiments will reveal how glycemic control modifies dry eye disease course due to diabetes mellitus.